1. Technical Field
The present invention relates to a pallet conveyor system and, more particularly, to a conveyor system that includes a conveyor to transport the pallets through vertical and horizontal curves.
2. Background
Manufacturing facilities, particularly automobile assembly plants in Europe, have for some time used moving pallets or skillets to convey large parts, such as vehicle bodies, throughout the facility. The pallets are commonly larger than the workpiece so as to permit a worker to ride the pallet along with the workpiece and to perform a production task as the pallet passes through a production area. When the referenced production task is complete for a pallet, the pallet moves through a delivery area and then to the next production area.
Many such facilities include multiple production areas on different levels. Accordingly, each pallet assembly, which includes the workpiece and pallet, is moved from production area to production area until all of the assembly steps are completed. The production areas within a facility are commonly separated from one another by delivery areas that are strategically positioned and configured within the overall system layout so as to provide readily accessible part storage, walkways, and other effective use of floor space.
In existing pallet conveyor systems, elevators are used to move the pallet assembly between floors, turntables rotate the pallet assembly, roll tables translate the pallet assembly along a linear path, and cross transfer tables move the pallet assembly along a perpendicular path. Moreover, various indexing stations, accelerators, and decelerators are used to provide proper pallet spacing in the production and delivery areas. These components are commonly intermixed with one another and combined with control systems to move the pallet assemblies between and through production areas located throughout the facility.
An exemplary layout might include first and second production areas oriented parallel to one another on a lower level of the building. The pallet assemblies are conveyed in a first direction through the first production area, raised to the second floor, moved into alignment with the second production area, lowered to the first floor, and then conveyed through the second production area in a direction opposite to that used in the first production area. A conventional conveyor system for such a layout would require friction drive assemblies at the end of the first production area to convey each pallet assembly to an elevator. The elevator would then raise the pallet and workpiece to the upper level of the building where an accelerating friction drive would move the pallet onto a roll table. The roll table then would convey the pallet to a cross transfer where the pallet is aligned with another elevator. An accelerator drive would then move the pallet into a second elevator for lowering the pallet to the lower level in alignment with the second production area. Another undocking drive would then move the pallet off of the second elevator and into the second production area.
While many of the elevators, transfer tables, roll tables, and turn tables may seem excessive if the only consideration were to move the pallet assemblies from one production area to the next along the shortest distance, important operational criteria such as the convenient storage of parts for the workers, maintaining walkways between and adjacent the production areas, and providing delivery areas where the pallet assemblies can be accumulated and/or indexed impact the overall pallet system layout. For example, indexing within delivery areas ensure the proper separation between pallets as they enter the next production area and provide for accumulation of pallets known as float. Sufficient float before a production area prevents the production area from having to immediately shut down due to lack of product should the preceding production area stop momentarily. Moreover, indexing may also be used in stations where the workpiece must be stationary in order to properly perform the production task.
Each of the above system components require drive, safety, and control units to ensure proper delivery of each pallet assembly to and through the respective production areas. Accelerating drives move the pallet assemblies into and out of the elevators and establish proper spacing between adjacent pallets in delivery areas. Docking drives ensure proper abutment of the pallets in the production areas. Finally, transfer tables, turntables, elevators, and friction drive assemblies move the pallets along, or change their orientation relative to, the path of movement. Each of the above components, and their associated controls, significantly impact the overall cost, complexity, and floor space requirements of conventional pallet conveyor systems.
As is described in greater detail below, the present invention eliminates many of the conveyor system components discussed above through the integrated use of a second conveyor system, preferably an inverted power and free conveyor. While some existing references do contemplate the use of a chain conveyor in combination with a conventional pallet conveyor, these references do not recognize the overall benefits attendant to the present invention nor the structure described and claimed herein. For example, U.S. Pat. No. 4,564,100 issued Jan. 14, 1986 to Moon, entitled xe2x80x9cCarrier Conveyor System,xe2x80x9d as well as U.S. Pat. No. 5,556,466 issued Sep. 17, 1996 to Martin et al., entitled xe2x80x9cCoating Plant,xe2x80x9d each relate to the use of a chain conveyor to deliver a pallet to a work area. However, these references do not disclose the specific features of the present invention nor the benefits thereof including, without limitation, using the chain conveyor to transport a pallet through vertical and horizontal curves, using the chain conveyor to deliver pallets into a work area wherein the pallets are placed in abutting engagement with one another, using an inverted power and free conveyor to move the pallets through delivery areas, the configuration of the transfer zone of the present invention, the extension of the free tracks in the power and free conveyor through the work area, and numerous other benefits such as those described below.
Finally, a particular feature of the present invention is the use of off-set and generally parallel free tracks within the production area in order to off-set the drive trolley from the load trolleys permitting the pallet assemblies to be moved from spaced engagement relative to one another in the delivery areas to abutting engagement in the production areas. While chain driven conveyor systems commonly include off-set and parallel free tracks in accumulation or bias areas, such conventional arrangements are not used to separate the drive trolley from the remaining load trolleys or otherwise takeup pallet spacings as the pallets enter production areas.
In view of the above, a need exists for a production operation that includes a chain conveyor system to effectively move pallets between production areas thereby providing cost savings over prior art systems and maximizing effective use of floor space.
Accordingly, an object of the invention is to include a chain conveyor that drives the pallet assemblies through delivery areas and a friction drive assembly that drives the pallet assemblies through production areas.
Another object of the present invention is to maintain the pallet assemblies spaced from one another in the delivery areas to permit the pallets to move more easily through vertical curves and horizontal turns and in abutting engagement with one another in the production areas.
A further object of the present invention is to provide a transfer zone where the pallets are moved from driving engagement with the chain conveyor and into driving engagement with the friction drive assembly. The transfer zone also moves the pallet assemblies between a spaced relationship relative to one another and abutting engagement.
A still further object of the present invention is to split the common free track of the chain conveyor system in the delivery area to offset drive trolley free and load trolley free tracks in the production area so as to permit the pallet assemblies to move from their spaced relationship in the delivery area to abutting engagement in the production areas.
Still another object of the present invention is to provide a pallet assembly with greater stability by including a yoke having rollers that engage the underside of the pallet assembly.
Yet another object of the present invention is to provide multiple sets of guide rails on the underside of the pallet and positioned to rollingly engage the rollers on the yoke to permit the pallet to be conveyed through a delivery area in a biased orientation.
In order to achieve the above advantages, the additional advantages discussed herein, and other advantages attendant to the improvement, the present invention is directed to a pallet conveyor system that includes a pallet assembly having a pallet and a workpiece coupled to the pallet, a production area where a production task is performed on the workpiece, and a delivery area wherein the pallet assembly is moved to or from the first production area. The pallet conveyor system also includes a first conveyor assembly to drive the pallet assembly through the first production area and a chain conveyor assembly to drive the pallet assembly through the first delivery area. The first conveyor assembly operably engages the pallet in the first production area but not in the delivery area. Conversely, the chain conveyor assembly drivably engages the pallet assembly in the delivery area but not in the production area. The present invention also includes a conveyor driven production operation which generally incorporates the above described pallet conveyor system as well as a method of moving a plurality of pallet assemblies through a production area.
The method relates to a method of moving a plurality of pallet assemblies through a production area wherein each of the plurality of pallet assemblies include a pallet and a workpiece coupled to each pallet. The production operation includes a first area and a delivery area wherein each pallet assembly is moved to or from the first area. The production operation also includes a first conveyor assembly drivably engaging the plurality of pallet assemblies in the first area and a power and free conveyor assembly drivably engaging the pallet assemblies in the delivery area. The power and free conveyor assembly includes a power track and a free track. The free track includes a common free track in the delivery area and a drive trolley free track offset from and generally parallel to a load trolley free track in the first area. The method includes the steps of maintaining the plurality of pallet assemblies spaced from one another in the delivery area and abutting adjacent pallet assemblies in the first area.
Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.